Concrete is a construction material made of a mixture of cement, sand, stone, and water. Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. Concrete is used to make pavements, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles.
In concrete technology an important field of interest is self compacting concrete (SCC), which flows and compacts itself due to gravity. Consequently, no external vibration or other compaction is needed. Hardened concrete will function as normal concrete in the structure. It is possible to produce very high performance concrete as self compacting concretes. Because compacting work is not needed, noise level during construction is lowered remarkable and one working phase is eliminated.
A problem with the SCC is the segregation and the sensitivity of the concrete to variations on raw materials. Due to extensive problems with low and normal strength SCC the use of SCC in low to normal strength concretes is not as wide as it could be. Segregation usually results in concrete with unacceptable properties. Segregation can be either water or aggregate segregation. In water segregation the water phase is separating when the cement particles are settling with time. Aggregate segregation occurs faster when aggregates are settling in the paste phase. Paste is the mixture of water, cement, other fine powders and admixtures. Small variations in raw material composition or moisture content can change SCC behavior dramatically. This lack of robustness in performance is also a hindrance for SCC use.
Accordingly there is a need for improved self-compacting concrete materials. Furthermore, there is a need to increase thixotrophy and particle suspendity in the wet state in standard concrete formulations.
Injection grouts are intended to be used with the pressure grouting technique. Requirements for these materials are among others high fluidity, low segregation and bleeding. In injection grouts very high fluidity is needed. In all applications strength requirements are not very high. That is why the water-cement ratio is in many applications very high. This leads to segregation problems and the penetration of grout is not sufficient.
There have been some attempts to solve the aforementioned problems with viscosity enhancing agents, for example with water soluble polysaccharides, such as welan gum or cellulose derivates. Patent applications GB 2 378 946 and WO 03/018505 disclose preparation of an admixture for cementitious compositions, wherein polysaccharide and/or nanosilica are used as viscosity modifying agents. Patent application US 2003/159391 relates to a lightweight concrete mixture, wherein soluble cellulose derivatives are used as viscosity enhancing agents. The use of e.g. welan gum as stabilizing admixture is widely known in the concrete industry.
Previously, cellulose fibers have been used in concrete materials to improve mechanical properties of materials: for example in US patent application 2005/112981 where cellulose fibers have been used to improve strength properties of dry specimens. Also, cellulose nanowhiskers have been studied as re-enforcement material in concrete, for example in a publication by Kuthcarlapati et al. (Metals Materials and Processes 20(3):307-314, 2008). In addition, the major aim in the publications mentioned above has been to improve mechanical properties of dry specimens i.e. not to influence on wet formulations. Also, in the above mentioned patent applications and publications, the used amount of cellulose fibers has been high.